Dendritic cells (DCs) are specialized for presenting antigens to naive or quiescent T cells. Consequently, DCs play a central role in modulating immunity in vivo (Steinman, 1991; Banchereau et al., 2000). Immunization using DCs loaded with selected antigens represents a powerful method of inducing immunity against pathogens or tumors (Gilboa et al., 1998; Dallal & Lotze, 2000; Fong & Engleman, 2000). Under appropriate conditions, DCs can also tolerize T cells and hence suppress an immune response against specific antigens (Steinman et al., 2000; Hackstein et al., 2001; Jonuleit et al., 2001).
The ability of DCs to induce an immune response requires antigen uptake, which occurs principally in non-lymphoid organs, followed by antigen presentation and activation of T cells in the lymph system. These separate functional roles are performed by immature DCs and mature DCs, respectively.
The signals for DC maturation are generally referred to as danger signals because they signal to the host the presence of a pathogen. Representative danger signals include various cytokines (e.g., IL-6, IL-1 or TNF-α), conserved pathogen determinants such as lipopolysaccharide (LPS), unmethylated CpG containing bacterial DNA, double stranded RNA, and components of cell debris such as heat shock proteins (HSP). See Celia et al. (1997) Curr Opin Immunol 9:10-16; Banchereau & Steinman (1998) Nature 392:245-252; Banchereau et al.(2000) Annu Rev Immunol 18:767-811; and Bell et al. (1999) Adv Immunol 72:255-324. Mature DCs are superior to immature DCs at eliciting an immune response (Morse et al., 1998; Nair et al., 1998). Immature DCs can also differentiate into tolerizing DCs, which disable cognate T cells from developing into an effector cell (Steinman et al., 2000; Hackstein et al., 2001; Jonuleit et al., 2001).
To elicit protective immunity, antigens of conventional vaccine formulations include: (a) protein; (b) attenuated or killed virus; (c) plasmid DNA; and (d) viral vectors. Optionally, a vaccine formulation also includes an adjuvant. Following administration of the vaccine to a subject, the antigen is captured by tissue resident immature DCs, which then mature.
More recently, vaccination strategies have been developed that accomplish antigen loading and maturation of DCs ex vivo. See e.g., Fong & Engleman (2000) Annu Rev Immunol 18:245-273. A typical approach for DC-based vaccination involves: (a) isolating and generating immature DCs from a subject; (b) loading the immature DCs with antigen; (c) culturing the immature DC in the presence of cytokines such as TNF-α, IL-6, IL-1β, and PGE2, whereby the immature DC undergoes maturation; and (d) re-administering the antigen-loaded, mature DC to the subject (Romani et al., 1994; Sallusto & Lanzavecchia, 1994).
Multiple factors contribute to the generation of an appropriate microenvironment conducive for optimal DC maturation, however, these factors remain poorly characterized and it is unclear whether provision of maturation agents in vitro faithfully recapitulates the inflammatory microenvironment that generates mature DCs in vivo.
Thus, there exists a long-felt need in the art to develop methods for immunization using DCs. To meet such a need, the present invention provides a method for preparing DCs that involves in situ DC maturation. Specifically, the method involves administering antigen-loaded DCs to a subject at a site of inflammation, to thereby promote DC maturation in situ. The present invention offers significant advantages over existing methods for DC-based immunization, including: (a) induction of DC maturation that more closely mimics endogenous DC maturation; and (b) elimination of procedural steps and reagents required for maturation of DCs ex vivo.